I believe they are being filtered. I'm not sure how dead auto-killed articles appear from the submitter's point of view, but I submitted an article yesterday that included the TSA acronym and it appeared to me without a comment box. This, and the absence articles on the front page, makes me think that filtering is in place.
I'm not complaining --- this is probably a fine policy. But it does complicate how one reads Matt's post. I think that HN actually does a lot behind the scenes to promote a better community, which is what keeps it as good as it is.